777 down.

[AtoZ]

My God! 17 pages on that ... People MUST have been bored stupid at the time

Answer is ... Yes, of course the aircraft would take off.

MW

i accept in theory that the plane would take off but would the tyres burst first?

in all of the theoretical arguments only a couple of posters looked at a real world scenario (empip)

im asking, and i do mean asking, because i saw a programe about concorde crashing.
part of the programe mentioned the take off speed which was higher due to the delta wing. they stated that the tyres had to especially made because normal tyres could not cope with the extra stresses involved.
that speed was 200 MPH or knots (i cant remember) i thought that a modern jet rotates at 130 ish mph or knots.
if this is so, with the added rolling resistance of the tyres, the heat increase over design rating causing more friction, would it definatly take off or would it crash before it could get there.

the op problem said aircraft, but if that were concorde, that wheel speed would be 400 mph/ or knots.
how fast would a military jet rotate at?
if we allow some for a safety margin on commercial aircraft, would that same margin apply to a light aircraft or a microlight.

you clearly know something about aircraft, certainly more than i do, so what do you think?
....................
i think of the firemen on duty, some could work a whole career and not have a plane down, imagine being on the opposite shift

 

[tim west]

I think the hypothetical model is based on the wheels having no resistance in their bearings and the tyres and indeed all parts of the aircraft able to withstand applied stresses.

 

[joe-90]

I don't think it's just to do with friction. I read somewhere that there are Einsteinian physics involved in regard to the deformation of space time. Which is why (apparently) a cyclist can balance when his bike is rolling rather than when it's stopped. Therefore no tyre can rotate at a speed up unto infinity.

 

[tim west]

Entirely possible in the 'special theory' not so sure about the 'general' one though.

 

[AtoZ]

i am fully in the take off camp but i was trying to apply some real world limitations to the problem

i can remember trying to drive my lego made cars with two magnets when i was a kid, that was long before i knew about a mag-lev train.

makes me think about a conveyer belt or a steam catapault system being used for aircraft, even if it were just to pull a plane up an incline so to give it a bit of a start. fuel savings might make it worth it..

sorry, i can get a bit sad thinking about things like this.

magnetic shock absorbers for cars, squeeze them and they will resist..
see what i mean

growing kiwi fruit on a tanker deck so that the journey to the sun is not wasted and environmental costs are reduced.
sail assisted ships..
endless

 

[tim west]

growing kiwi fruit on a tanker deck so that the journey to the sun is not wasted

Any journey to the sun would be a waste as you'd burn up long before you got there.

 

[noseall]

this is the way i look at it. and yes, i do believe the aircraft will take off.

but....


just for a moment forget the engines are running, and the plane is still stood on a rolling conveyer.

someone switches on the conveyor, and the plane lets his handbrake off, and someone has strung a cable across the path of the aircraft stopping it from travelling backwards.

the aircraft will stay still but the wheels will rotate as the conveyor moves backwards.

if someone was to remove the cable restraint then it will allow the plane to shoot backwards, but if he engages thrust to stop the aircraft from doing this.....

i do still think it will take off though.

 

[Trazor]

i am fully in the take off camp but i was trying to apply some real world limitations to the problem

You have to remember this is purely a hypothetical question, any attempt to replicate it in a real world scenario is fraught with problems.

Pure and simply the jets/props produce thrust relative to the atmosphere, and its irrelevant whether the wheels are touching anything or not.

 

[blondini]

It doesn't matter what the aircraft is. The hypothetical conveyor runway is moving backwards and no matter how fast the aircraft travels relative to the conveyor surface, the conveyor matches to the wheelspeed of the aircraft. The aircraft engines are exerting a forward thrust, but the conveyor is exerting an equal and opposite reverse thrust against the aircraft solely through the rolling resistance of the aircraft wheels.The aircraft therefore cannot move forward relative to it's own position in space and can gain no airspeed. If it did move forward relative to it's own position it would mean the hypothetical conveyor wasn't matching the wheelspeed.

Obviously on a real aircraft, the wheels and tyres would be unable to survive the speeds required to create sufficient drag to counter the full thrust of the engines, but this is just hypothetical.

 

[noseall]

i bet this theory would be rather difficult to apply to a harrier vtol jet.

 

[blondini]

this is the way i look at it. and yes, i do believe the aircraft will take off.

but....


just for a moment forget the engines are running, and the plane is still stood on a rolling conveyer.

someone switches on the conveyor, and the plane lets his handbrake off, and someone has strung a cable across the path of the aircraft stopping it from travelling backwards.

the aircraft will stay still but the wheels will rotate as the conveyor moves backwards.

if someone was to remove the cable restraint then it will allow the plane to shoot backwards, but if he engages thrust to stop the aircraft from doing this.....

i do still think it will take off though.

Say the conveyor is moving backwards at a walking pace and the the pilot uses just enough thrust to move keep the plane from moving backwards with the conveyor. Double the speed of the conveyor and more thrust will be needed just to keep the aircraft from moving backwards. The hypothetical conveyor can keep increasing it's speed...

 

[tim west]

Noseall, you forget one thing removing the cable will achieve nothing in your scenario as the plane would remain static and NOT roll backwards, remember the wheels bearings have no friction for all intents and purposes they are free wheeling and not attached to the axle of the undercarriage.therefore the wheels would turn but the aircraft would stay static as no force is acting on it.

Blondini the scenario with thrust is slightly different as now a force is acting on the aircraft.

 

[noseall]

remember the wheels bearings have no friction for all intents and purposes they are free wheeling

well if you factor this statement into the equation then the plane will take off.

 

[Trazor]

Say the conveyor is moving backwards at a walking pace and the the pilot uses just enough thrust to move keep the plane from moving backwards with the conveyor. Double the speed of the conveyor and more thrust will be needed just to keep the aircraft from moving backwards. The hypothetical conveyor can keep increasing it's speed...

That would be true if you put a car on the conveyor, as it is DRIVEN by its wheels.
A plane provides its thrust against the air surrounding it.

 

[AtoZ]

growing kiwi fruit on a tanker deck so that the journey to the sun is not wasted

Any journey to the sun would be a waste as you'd burn up long before you got there.

i saw thunderbirds and they went to the sun to save some other spaceship... they made it back ok..

the acting from alan tracey was brilliant in that episode.. worth an oscar